1. Field of the Invention
The present invention relates to a printer control unit, printer control method, printer control program, medium storing printer control program, printer, and printing method.
2. Description of the Prior Art
An ink-jet printer squirts ink droplets onto pixels arranged in dot-matrix array through the nozzles of the print head, thereby performing printing. The nozzles of the print head are arranged at a constant interval in the paper feed direction, and they constitute the nozzle column. Usually, an ink-jet printer has one or more nozzle columns for each color ink.
The nozzle interval is not related directly with the printing resolution; however, the nozzle interval in the paper feed direction usually corresponds to the printing resolution. For example, it will be possible to arrange nozzles (for one color ink) in two columns, offset by half the nozzle spacing, so that each of two columns prints one line of pixels alternately. In this case, each nozzle squirts as many ink droplets as necessary to completely fill one line.
With the above-mentioned structure, the first column of nozzles and the second column of nozzles are allotted alternately to one line having pixels arranged in dot matrix array, and the nozzles squirt ink droplets of specified color to print a completely filled image as desired. Once the printing resolution based on the nozzle interval is established, it is possible to prepare image data (for printing data) according to the printing resolution.
There is another structure designed to eliminate “graininess” resulting from an ink-jet printer. With this structure, nozzles in the first column squirt a dark color ink and nozzles in the second column squirt a light color ink.
It is assumed that the distance between adjacent nozzles in each column is equivalent to 180 dpi and the distance between the first and second columns is equivalent to 360 dpi. It is further assumed that the size of a dot formed by an ink droplet is equivalent to 360 dpi. In this case, when the print head traverses the paper, each line of pixels is printed with a dark color ink and a light color ink alternately. Subsequently, printing is repeated, with the print head shifted by a distance equivalent to 360 dpi, so that the line for a dark color ink and the line for a light color ink are exchanged each other. In this way it is possible to print each line of pixels with a dark color ink and a light color ink, thereby eliminating graininess. In this case, the image data corresponds to the printing resolution of 360 dpi as a matter of course.
The conventional high-resolution printing mentioned above employs nozzles arranged zigzag in two columns to eliminate graininess. The disadvantage of this system for high resolution is a low print speed. Monochrome printing with black ink squirted from nozzles arranged zigzag in two columns permits high-speed printing with 360-dpi resolution by one print head traverse; however, this advantage is offset by slow printing with a dark color ink and a light color ink which are squirted separately twice.